In a conventional seat adjusting unit for a vehicle disclosed in JP6071868B (hereinafter referred to as Patent Document 1), one end of a drive shaft protruding from one end of a housing is connected to an output shaft of a motor. One end of a hub located at the outer side of the housing is joined to one end face of a spindle nut and the other end of the hub is located within the housing. A threaded spindle is fitted into the spindle nut so as to mesh therewith. The threaded spindle is connected to a seat, thereby being prevented from rotating. A worm wheel is formed at the other end of the hub. The worm wheel meshes with a worm arranged at the other end of the drive shaft. Such drive shaft is arranged so as to intersect with the hub so as to be perpendicular to a longitudinal axial line of the hub. According to the above configuration of the seat adjusting unit, when the motor is driven, the drive shaft and the worm gear integrally rotate with each other, thereby rotating the worm wheel and the spindle nut. Consequently, the threaded spindle axially moves, thereafter moving the seat in a longitudinal direction of the vehicle.
In a front vertical mechanism of a power seat for a vehicle described in JP2005028955A (hereinafter referred to as Patent Document 2), an axially unmovable nut member is provided in a gearbox so as to be rotatable therewithin. A worm wheel is formed around an outer circumference of the nut member. A worm provided on an output shaft of a motor meshes with the worm. A threaded bar is screwed with an inner circumferential surface of the nut member. One end of the threaded bar is attached to a link with a pin so as to be rotatable. Such threaded bar is arranged to intersect with the motor so as to be perpendicular thereto. According to the above configuration of the front vertical mechanism, when the motor is driven, the worm rotates, thereby rotating the worm wheel. Accordingly, the nut member rotates along with the rotation of the worm wheel, thereby axially moving the threaded bar. Thus, the link rotates and a front portion of a seat cushion is moved upward and downward while rotating about the pin.
In a seat lifter of a power unit adapted to be mounted on a seat for a vehicle, described in JP6011227Y (hereinafter referred to as Patent Document 3), a worm wheel and a first screw wheel are supported within a gearbox so as to rotate concentrically with each other. A second screw wheel is also supported within the gearbox. The second screw wheel is located perpendicular to the first screw wheel so as to mesh therewith. A worm provided on an output shaft of a motor meshes with the worm wheel. A screw shaft is axially attached to the second screw wheel. Nut blocks are screwed with the screw shaft. A lever and a link are connected to each of the nut blocks. Such screw shaft is arranged in parallel to the motor. According to the above configuration of the seat lifter, when the motor is driven, the worm rotates and the worm wheel integrally rotates with the first screw wheel, integrally rotating the second screw wheel with the screw shaft. Accordingly, the nut blocks axially move, thereby rotating the lever and tilting the link. Consequently, the seat lifter is moved upward and downward.
In the mechanism described in Patent Document 1, the motor and the threaded spindle are arranged in an L-shape or a T-shape. When such mechanism is arranged toward the center of a seat back from a lateral side of the seat back, for example, in order to apply the mechanism to an angle adjusting unit used for an upper seat back portion of the seat back, an occupant may contact the mechanism. Accordingly, the mechanism is required to be arranged at the lateral side of the seat back so as to extend along a rearward direction of the seat back in a longitudinal direction of the vehicle in order to prevent the occupant from contacting the mechanism. However, when the mechanism is arranged at the lateral side, the following issues may occur in designing the seat layout. In this case, the thickness of the seat back is increased, thereby resulting in a reduction of an internal space of the vehicle. Furthermore, in the mechanism described in Patent Document 2, the motor and the threaded bar are arranged in an L-shape or a T-shape. Accordingly, when the mechanism is applied to the angle adjusting unit used for the upper seat back portion, the above-mentioned issues may occur in the same way as described in Patent document 1. In the mechanism described in Patent Document 3, although the motor and the screw shaft are arranged in parallel to each other, a projected area of the mechanism seen from the axial direction is large. Accordingly, the above-mentioned issues may occur. In addition, the worm, the worm wheel, and a pair of the first and second screw wheels are required for the mechanism, so that the number of applied components increases, thereby resulting in cost increase.
A need thus exists for a motion converting drive mechanism and a seat apparatus for a vehicle including the motion converting drive mechanism, which are not susceptible to the drawback mentioned above.